Iron (Fe) is an essential mineral nutrient and an important factor for the composition of natural plant communities. Low Fe availability in aerated soils with neutral or alkaline pH has led to the evolution of elaborate mechanisms that extract Fe from the soil solution. In Arabidopsis (), Fe is acquired by an orchestrated strategy that comprises mobilization, chelation, and reduction of Fe prior to its uptake. Here, we show that At3g12900, previously annotated as scopoletin 8-hydroxylase (S8H), participates in Fe acquisition by mediating the biosynthesis of fraxetin (7,8-dihydroxy-6-methoxycoumarin), a coumarin derived from the scopoletin pathway. S8H is highly induced in roots of Fe-deficient plants both at the transcript and protein levels. Mutants defective in the expression of showed increased sensitivity to growth on pH 7.0 media supplemented with an immobile source of Fe and reduced secretion of fraxetin. Transgenic lines overexpressing exhibited an opposite phenotype. Homozygous mutants grown on media with immobilized Fe accumulated significantly more scopolin, the storage form of scopoletin, supporting the designated function of S8H in scopoletin hydroxylation. Fraxetin exhibited Fe-reducing properties in vitro with higher rates being observed at neutral relative to acidic pH. Supplementing the media containing immobile Fe with fraxetin partially rescued the mutants. In natural Arabidopsis accessions differing in their performance on media containing immobilized Fe, the amount of secreted fraxetin was highly correlated with growth and Fe and chlorophyll content, indicating that fraxetin secretion is a decisive factor for calcicole-calcifuge behavior (i.e. the ability/inability to thrive on alkaline soils) of plants.

Root hairs are highly specialized cells found in the epidermis of plant roots that play a key role in providing the plant with water and mineral nutrients. Root hairs have been used as a model system for understanding both cell fate determination and the morphogenetic plasticity of cell differentiation. Indeed, many studies have shown that the fate of root epidermal cells, which differentiate into either root hair or non-hair cells, is determined by a complex interplay of intrinsic and extrinsic cues that results in a predictable but highly plastic pattern of epidermal cells that can vary in shape, size and function. Here, we review these studies and discuss recent evidence suggesting that environmental information can be integrated at multiple points in the root hair morphogenetic pathway and affects multifaceted processes at the chromatin, transcriptional and post-transcriptional levels.

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In concert with oxygen, soil alkalinity strongly restricts the availability of iron, an essential nutrient with a multitude of functions in living organisms. In addition to its role in mitochondrial energy metabolism and as a cofactor for enzymes, in plants iron also plays key roles in photosynthesis and is required for chlorophyll biosynthesis. The ability to thrive in calcareous soils, referred to as calcicole behaviour, is the readout of an amalgam of traits of which efficient foraging of iron is a decisive factor. Recently, the well-established concept of two distinct iron uptake strategies, phylogenetically separating grasses from other land plants, was expanded by the discovery of auxiliary mechanisms that extend the range of edaphic conditions to which a species can adapt. Secretion of a tailor-made cocktail of iron-mobilising metabolites into the rhizosphere, the composition of which is responsive to a suite of edaphic and internal cues, allows survival in calcareous soils through a competitive iron acquisition strategy, which includes intricate interactions with the consortium of associated microorganisms in, on, and around the roots. This versatile, reciprocal plant-microbiome interplay affects iron mobilisation directly, but also collaterally by impacting growth, fitness, and health of the host. Here, we review the mechanisms and the multifaceted regulation of iron acquisition in plants, taking into consideration the specific constraints associated with the uptake of iron from alkaline soils. Knowledge on how plants extract iron from such soils sets the stage for a better understanding of essential ecological processes and for combatting iron malnutrition in humans.

Isobaric tags for relative and absolute quantitation (iTRAQ) is a technology that utilizes isobaric reagents to label the primary amines of peptides and proteins and is used in proteomics to study quantitative changes in the proteome by tandem mass spectrometry . Here, we present an adaptation of the iTRAQ experimental protocol for plants that allows the identification and quantitation of more than 12,000 plant proteins in Arabidopsis with a false discovery rate of less than 5 %.